Dielectric directional coupler



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I ELECTRIC DIRECTIONAL COUPLER Filed May 16, 1967 5 Sheets-Sheet 5 United States Patent 3,493,897 DIELECTRIC DIRECTIONAL COUPLER Adnan T. Hayany, Kansas City, Mo., assignor to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Filed May 16, 1967, Ser. No. 638,949 Int. Cl. H01p /14 US. Cl. 333 13 Claims ABSTRACT OF THE DISCLOSURE An adjustable, broad-band directional coupler of the cross-guide type employs a pair of solid dielectric waveguides of rectangular cross-section. Adjacent superposed wide walls of the waveguides are maintained at an invariant spacing from each other, The coupling amplitude may be varied, while maintaining a high value of directivity, by varying the orientation of a pair of vanes rotatably mounted between the adjacent wide walls at a pair of spaced positions within the superposed region.

BACKGROUND OF THE INVENTION Directional couplers are frequently employed between two portions of a high frequency transmission system to permit a main electromagnetic wave propagating in one direction along one such portion (the primary waveguide), to induce an auxiliary wave traveling in a preferred direction along the other portion (the secondary waveguide). It is often desirable, for test and monitoring purposes, to be able to vary the coupling between the primary and secondary waveguides (i.e., the relative am plitudes of the main and auxiliary waves). Such coupling variation should be accomplished while maintaining, in the secondary guide, a high directivity (i.e., a large ratio between the amplitude of the auxiliary wave and that of a spurious wave induced in the secondary waveguide by the main wave and traveling in the non-preferred direction).

The desirability of providing an adjustable waveguide directional coupler has been long recognized, and several configurations has been devised for use in hollow, conductively bounded (i.e., metallic) waveguide systems. US. Patents 2,804,597 (1957) and 2,989,559 (1959) disclose examples of adjustable directional couplers formed from metallic waveguide.

For certain applications, it is desirable to provide a directional coupler that can be constructed of solid dielectric waveguide. Such a device may become increasingly useful in long distance, high frequency transmission systerns, where the use of solid dielectric guide in place of metallic guide can result in looser tolerances, greater power handling capacity, increased bandwidth, and relatively low loss per unit length. For more immediate applications, similar advantages may be obtained by employing solid dielectric couplers, when suitably modified, as discrete components in existing metallic systems.

While dielectric directional couplers are not unknown [see, e.g., US. Patent 2,794,959 (1957)] the coupling of such devices can normally be adjusted, without a severe loss in directivity, only by moving the primary and secondary waveguides closer together or farther apart. This type of directional coupler cannot be conveniently adjusted when the primary and secondary waveguides must be relatively fixed at all times.

The particular problem treated by the present invention is that of providing a solid dielectric, high-directivity directional coupler whose coupling amplitude may be adjusted without physically varying the spacing between the coupled waveguides.

3,493,897 Patented Feb. 3, 1970 SUMMARY OF THE INVENTION One solution to this problem is the provision of a dielectric cross-guide directional coupler constructed in accordance with the instant invention. In one embodiment, a pair of rectangular dielectric waveguides are superposed in mutually perpendicular, electromagnetically coupled relation with their wider walls parallel to and fixedy spaced from each other. A spaced pair of planar metallic vanes are rotatably mounted in the common space between the superposed wide walls of the waveguides. The value of coupling may be set, and precisely varied, by orienting the vanes in a desired angular relationship and rotating the vanes by equal angular increments in a plane parallel to the wide walls.

The coupling of this device, at any given setting of the vanes, remains substantially constant over a broad band of frequencies. Moreover, the directivity of the device remains consistently high over a wide range of vane settings as well as over the broad band.

BRIEF DESCRIPTION OF THE DRAWING The nature of the present invention and its various advantages will appear more fully by referring to the following detailed description in conjunction with the appended drawing, in which:

FIG. 1 is a plan view of a dielectric cross-guide directional coupler constructed in accordance with the invention;

FIG. 2 is an elevational section taken along line 22 of FIG. 1;

FIG. 3 is a perspective view of one of the vanes employed in the coupler of FIG. 1;

FIG. 4 is an elevational view, similar to FIG. 2, but including a ganging arrangement for simultaneously rotating a pair of vanes;

FIG. 5 is a set of curves showing typical variations of coupling and directivity with frequency for the arrangement of FIG. 1;

FIGS. 6-9 are a set of plan views showing different relative orientations of the vanes;

FIGS. 10-13 are a set of curves showing typical variations of coupling and directivity with frequency for the arrangements of FIGS. 69, respectively;

FIG. 14 is a perspective View of a directional coupler constructed in accordance with the invention and provided with transitions to permit its use in a metallic waveguide system; and

FIG. 15 is a sectional view taken along line 15--15 of FIG. 14.

DETAILED DESCRIPTION Referring now in more detail to the drawing FIG. 1 depicts an illustrative directional coupled 26 constructed in accordance with the invention. The coupler includes a pair of crossed elongated waveguides 27 and 28 having a pair of longitudinal axes 29' and 31, respectively. The waveguides 27 and 28 are formed from continuousfruns of low-loss, homogeneous, solid dielectric material (such as polystyrene) of identical cross-sectional dimensions. The waveguide 27 is provided with an input port W which is coupled (by means not shown) to incoming electromagnetic waves and with an output port X spaced from I the port W. The waveguide 28 is provided with a principal or coupling output port Y and an auxiliary or directivity output port Z. The ports X, Y and Z are assumed to be suitably terminated (by means not shown).

As shown best in FIG. 2, the waveguide 27 has a rectangular transverse cross-section defined by a pair of opposed wide walls 33 and 34, of width A, joined by a pair of opposed narrow walls 36 and 37, of width B. The dimensions A and B are chosen to support the TE wave mode over a wide frequency range, which is assumed to 3 be centralized in the 3.6-4.3 KMC band. For example, a waveguide cross-section having A=2.40" and B=1.24" has been found satisfactory. It will be understood that the waveguide 28 has corresponding cross-sectional dimensions.

Since the waveguides 27 and 28 have non-conductive boundaries, electromagnetic waves propagating in each will have finite field components extending transversely beyond the periphery of the associated waveguide into the surrounding air. This serves two functions: (a) to facilitate electromagnetic interaction between the waveguides when placed in coupling relation, and (b) to increase the effective cross-section of each waveguide and thus its potential bandwidth.

The wider walls 33 and 34 of the waveguide 27 are oriented parallel to a pair of corresponding wider walls 38 and 39 of the waveguide 28 by means of an interconnecting pair of elongated dielectric pins 41 and 42, which extend perpendicular to the wider walls. The pins 41 and 42 serve to maintain the waveguides in fixedly spaced, electromagnetically coupled relation, with the longitudinal axes 29 and 31 (FIG. 1) of the waveguides extendingperpendicular to each other. With this arrangement, intermediate portions of the waveguides (i.e., portions between ports W-X and Y-Z, respectively) are superposed to form a common coupling region 43 therebetween of substantially sq-uare cross-section.

The pins 41 and 42 have cross-sectional areas which are small compared to those of the waveguides 27 and 28, and are formed from polystyrene or other dielectric material having substantially the same dielectric constant as that forming the waveguides.

The pins 41 and 42 respectively extend perpendicularly through a pair of spaced apertures 44 and 46 in the waveguide 28, and terminate at the bottoms of a pair of corresponding seating recesses 47 and 48 within the wave guide 27. The diameter of the pins 41 and 42 are chosen to form a reasonably tight fit within the waveguides 27 and 28 to prevent relative movement of the latter, but not tight enough to fully preclude rotation of the pins about their own axes. Such rotation may be imparted, e.g., by a screwdriver or the like (not shown) through a pair of suitable slots 49 and 51 cut in the upper ends of the pins 41 and 42, which terminate flush with the wide wall 38 of the waveguide 28.

Referring to FIG. 1, the pins 41 and 42 are symmetrically disposed within the common region 43 and are positioned in transversely spaced relation to each of the longitudinal axes 29 and 31. In particular, the pins 41 and 42 are spaced from each other by distances F and G, which are measured parallel to the axes 29 and 31 respectively. Preferably, each of the distances F and G is equal to an odd number of quarter wavelengths in the waveguides 27 and 28 at a mean frequency of operation.

The length of the pins 41 and 42 is chosen so that the adjacent wide walls 33 and 39 (FIG. 2) of the waveguides 27 and 28 are separated by a fixed distance K in the common region 43. To obtain maximum directivity in the coupler 26, the distance K is preferably made greater than a quarter Wavelength in the waveguides 27 and 28, but less than half the width A of their wide walls.

A pair of planar, substantially rectangular metallic vanes 52 and 53 are individually aflixed to the pins 41 and 42 intermediate their ends within the common region 43. As shown best in FIG. 3, each vane has a thickness H, a width D approximately equal to K, and a length E. In the mounted position shown in FIGS. 1-2, the dimension E of each vane extends in a plane parallel to the wider walls 33-34 and 38-39, and the dimension D extends parallel to the axes of the pins.

The thickness of each vane may be greater than the diameter of the associated pin, in which case the vane is provided with a central aperture 54 (FIG. 3) extending completely therethrough parallel to the dimension D for receiving the pin. The diameter of the aperture 54 should be chosen to form a sufficiently tight fit with the periphery of the pin to preclude relative movement of the vane and pin. Alteinately, if desired, the thickness of the vane may be less than the diameter of the pin, in which case the vane may be atfixed to the pin in any suitable manner such as through a centralized longitudinal slot (not shown) in the pin. In any event, the dimension H is preferably at least but less than D/ 2.

The center of the vane 52 is displaced to the left of the longitudinal axis 29 as viewed in FIG. 1, i.e., toward the coupling port Y of the waveguide 28. On the other hand, the center of the vane 53 is displaced to the right of the longitudinal axis 29, i.e., toward the directivity port Z of the waveguide 28. In general, the direction of coupling in the arrangement of the invention, when electromagnetic wave energy is introduced into port W, is in the direction of deviation of the nearest vane (i.e., the vane 52) from the longitudinal axis 29'. Thus, coupling occurs between ports W and Y, while ports W and Z are ideally isolated.

The coupling and directivity of the arrangement of FIGS. l2 are principally determined by two parameters: (1) the angle defined by the intersection, if any, of the planes of the vanes; and (2) the orientation of the vanes with respect to the wide walls of the waveguides and, more particularly, with respect to the longitudinal axes 29 and 31.

The vanes may be oriented in any desired manner by adjusting the angular position of the pins 41 and 42 via the slots 49 and 51. In FIG. 1, for example, the vanes are oriented so that the vane 36 is disposed at at 45 angle to both of the longitudinal axes 29 and 31, and the vane is parallel to the longitudinal axis 29.

The directivity of the coupler 26 may be experimentally set at a desired high value by initially adjusting the angle between the vanes, after which the coupling may be varied without undue loss in directivity by rotating both vanes through equal angular increments. The latter may be conveniently accomplished in separate steps, or, alternately, may be done simultaneously with the use of a ganging arrangement such as that shown in FIG. 4. This arrangement includes a pair of disengageable mated gears 53 and 54 that are respectively affixed to a pair of upwardly extending projections 55 and 56 of the pins 41 and 42. The gears may be rotated by any suitable means (not shown), as by a portion 57 of the projection 56 which extends through the gear 54.

As shown in FIG. 1, a fine adjustment of the optimum frequency band of the coupler 26 may be obtained by providing the waveguides 27 and 28 with a plurality of thin metallic sleeves 58-58 individually disposed between the ports W, X, Y and Z and the common region 43. Each sleeve 58 conforms in shape to, and contacts, the rectangular transverse periphery of the associated waveguide. Each sleeve is further arranged for movement parallel to the longitudinal axis of the associated waveguide for adjustment purposes. For optimum operation in the band of frequencies specified above, the length of each sleeve should be A" to /2 Typical variations of coupling and directivity with frequency in the coupler 26 when the vanes are oriented as shown in FIG. 1 are depicted in FIG. 5. The characteristics shown were obtained with a coupler having the following dimensions: A-=2 B=1 D=K= E=1%; F=1%; G-=l%"; H=

FIG. 6 shows an alternative vane orientation wherein the vane 52 is parallel to the longitudinal axis 31 and the vane 53 is parallel to the longitudinal axis 29. The variation of coupling and directivity as a function of frequency with the vanes in this position is given in FIG. 10.

FIGS. 1l-13 illustrate the variation in coupling obtained by setting the angle between the vanes 52 and 53 to zero (i.e., making them parallel) and then rotating the vanes to the positions respectively shown in FIGS. 7-9. In FIG. 7, for example, the vanes are oriented parallel to the longitudinal axis 29; in FIG. 8, at 45 to each of the axes 29 and 31; and in FIG. 9, parallel to the axis 31.

It will be apparent from an inspection of the curves of FIG. 5 and FIGS. -13 that for any given setting of the vanes, the coupling remains substantially constant over the 3.74.2 frequency band. Moreover, the directivity of the coupler remains consistently high (e.g., greater than 30 db) over a wide range of vane settings as well as over the frequency band.

FIGS. 14-15 illustrate an arrangement by which the coupler 26 may be modified for use in a hollow waveguide transmission system. The ports W and X of the waveguide 27 are respectively joined by suitable flanges to a pair of hollow metallic waveguide runs 59 and 60 of similar cross-section. Similarly, the ports Y and Z of the waveguide 28 are joined to a pair of similar metallic runs 61 and 62. The resulting mismatch at the ports of each of the waveguides is compensated with the use of a pair of longitudinally extending reflectors 63 and 64, which are individually associated with the opposite ports of each waveguide. The reflectors 63 and 64 may be of the type described and claimed in applicants copendin-g application S.N. 608,149, filed Jan. 9, 1967.

As shown best in FIG. 15, the reflector 63 associated with the waveguide 28 extends to the right from port Y. The reflector 64 extends to the left from the opposite port Z. The reflector 63 is located below the lower wider wall 39, and the reflector 64 is located above the upper wider wall 38. The transverse spacing between the reflector 63 and the lower wide wall 39 decreases monotonically with longitudinal distance along the waveguide from a maximum at the port Y. Similarly, the transverse spacing between the reflector 64 and the upper wall 38 decreases monotonically with longitudinal distance along the waveguide from the opposite port Z. It will be understood that the relative arrangement of the reflectors 63 and 64 associated with the waveguide 27 (FIG. 14) is identical to that just described in connection with the waveguide 28, and that the arrangement shown in FIGS. 14-15 will function in the manner identical to that of FIGS. 1-2.

It will be further understood that the above-described arrangements of elements are merely illustrative of the principles of the invention and that many other modifications can be made without departing from the spirit and scope of the invention.

What is claimed is:

1. In a variable directional coupler:

first and second elongated sections of solid dielectric waveguide;

means for mounting the sections with predetermined surfaces thereof disposed in fixedly spaced relation to define a common superposed region; and

means for adjustably coupling the fixedly spaced surfaces at a pair of spaced locations within the common superposed region.

2. In a variable directional coupler for dividing an input microwave signal into a plurality of output signals:

a first elongated, solid dielectric waveguide for receiving the microwave signal at one end and trans- =mitting a first portion of the received signal from the opposite end to form a first output of the coupler;

a second elongated, solid dielectric waveguide for directing a second portion of the input signal to one end thereof to form a second output of the coupler;

means for transversely supporting the first and second waveguides in overlapping relation with a fixed spacing therebetween;

means interposed between the overlapping regions of the waveguides for coupling the second portion of the input signal from the first waveguide toward the one end of the second Waveguide, the coupling means including a pair of planar vanes symmetrically spaced from the longitudinal axes of both of the waveguides; and

6 means for varying the orientation of the planes of the vanes with respect to the overlapping regions to change the ratio between the first and second outputs ot' the coupler.

3. variable crossguide directional coupler, which comprises:

a pair of elongated solid dielectric waveguides;

means for mounting intermediate portions of the waveguides in fixedly spaced, superposed relation with the axes of the waveguides extending in mutually perpendicular directions:

first and second planar vanes individually carried by the mounting means at a pair of spaced locations in the region between the superposed intermediate portions; and

means for varying the orientation of the planes of the vanes with respect to the superposed intermediate portions.

4. A variable crossguide directional coupler, which comprises:

a pair of elongated solid dielectric waveguides of rectangular cross-section;

means for mounting intermediate portions of the waveguides in fixedly spaced, superposed relation with the axes of the Waveguides extending in mutually perpendicular directions and 'with a pair of wider Walls of the respective waveguides disposed in adjacent parallel relation, the mounting means including first and second rods extending perpendicularly between the adjacent wider walls and rotatably received within the waveguides at a pair of spaced locations within the common region between the superposed intermediate portions;

first and second planar vanes aflixed to the rods between the adjacent wider walls, the planes of the vanes being perpendicular to the wider walls; and means for rotating the rods.

5. A coupler as defined in claim 4, in which the rods are symmetrically disposed within the common region and transversely displaced from the axes of the waveguides, the rods being separated by one-quarter wavelength in the waveguides as measured along at least one of the mutually perpendicular directions.

6. A coupler as defined in claim 4, in which the vane dimension parallel to the wider walls is greaterthan the vane dimension perpendicular to the wider walls.

7. A coupler as defined in claim 4, further comprising a longitudinally adjustable sleeve surrounding at least one of the waveguides at a location displaced from the common region for varying the frequency response of the coupler.

8. A coupler as defined in claim 4, in which the superposed intermediate portions are spaced by greater than one quarter wavelength in the waveguides.

9. A coupler as defined in claim 4, in which the vanes are formed from conductive material.

10. A coupler as defined in claim 4, in which the planes of the vanes are parallel.

11. A coupler as defined in claim 4, in which the planes of the vanes are perpendicular.

12. A coupler as defined in claim 4, in which the planes of the vanes form an acute angle.

'13. A coupler as defined in claim 4, further comprising first and second substantially identical, longitudinally extending reflectors transversely spaced from opposite wider walls of one of the waveguides, the first reflector extending from one end of the waveguide to a first intertermediate cross-section thereof, the second reflector extending from the other end of the waveguide to a second intermediate cross-section thereof,'the spacing of each reflector from the adjacent wider wall decreasing monotonically with longitudinal distance from the associated end.

(References on following page) 7 8 References Cited HERMAN KARL SAALBACH, Primary Examiner UNITED STATES PATENTS MARVIN NUSSBAUM, Assistant Examiner 2,794,959 5/1957 Fox 333-10 FOREIGN PATENTS 731,473 5/1955 Great Britain.

Parent NQJQQQLEQY 1 UNITED sTATEs'PAT-ENT OFFICE 3 CERTIFICATE OF CORRECTION am: February 3.. 1970 Inventor(s) Adnan T. Hayany It is certified that error appears in the above-identified parent and that said Letters Patent are hereby corrected as shown below:

Column 1, line '46 change "2,989,559" to read 9 9559 Column 2, line 53, cancel "coupled" and insert --coupler--.

Column 4, line 42, change "53"- to --55-.

Column 5, line 23, change the period to a comma,

ang add now U.S. patent 3,452,302 issued June 24. 19 9- 0 Drawing. FIG. 4., change "53" to --55-.

Signed and sealed this 6th day of April 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting Officer WILLIAM E. SCI-IUYLER, JR. Commissioner of Patents 

